968 research outputs found
A comparison of two closely-related approaches to aerodynamic design optimization
Two related methods for aerodynamic design optimization are compared. The methods, called the implicit gradient approach and the variational (or optimal control) approach, both attempt to obtain gradients necessary for numerical optimization at a cost significantly less than that of the usual black-box approach that employs finite difference gradients. While the two methods are seemingly quite different, they are shown to differ (essentially) in that the order of discretizing the continuous problem, and of applying calculus, is interchanged. Under certain circumstances, the two methods turn out to be identical. We explore the relationship between these methods by applying them to a model problem for duct flow that has many features in common with transonic flow over an airfoil. We find that the gradients computed by the variational method can sometimes be sufficiently inaccurate to cause the optimization to fail
Lifshitz fermionic theories with z=2 anisotropic scaling
We construct fermionic Lagrangians with anisotropic scaling z=2, the natural
counterpart of the usual z=2 Lifshitz field theories for scalar fields. We
analyze the issue of chiral symmetry, construct the Noether axial currents and
discuss the chiral anomaly giving explicit results for two-dimensional case. We
also exploit the connection between detailed balance and the dynamics of
Lifshitz theories to find different z=2 fermionic Lagrangians and construct
their supersymmetric extensions.Comment: Typos corrected, comment adde
On Eigenvalue spacings for the 1-D Anderson model with singular site distribution
We study eigenvalue spacings and local eigenvalue statistics for 1D lattice
Schrodinger operators with Holder regular potential, obtaining a version of
Minami's inequality and Poisson statistics for the local eigenvalue spacings.
The main additional new input are regular properties of the Furstenberg
measures and the density of states obtained in some of the author's earlier
work.Comment: 13 page
Taking Stock of Common Core Math Implementation: Supporting Teachers to Shift Instruction: Insights from the Math in Common 2015 Baseline Survey of Teachers and Administrators
In spring 2015, WestEd administered surveys to understand the perspectives on Common Core State Standards-Mathematics (CCSS-M) implementation of teachers and administrators in eight California school districts participating in the Math in Common (MiC) initiative. From this survey effort, we were able to learn from over 1,000 respondents about some of the initial successes and challenges facing California educators attempting to put in place and support new -- and what some consider revolutionary -- ideas in U.S. mathematics education
On the Fredholm property of bisingular pseudodifferential operators
For operators belonging either to a class of global bisingular
pseudodifferential operators on or to a class of bisingular
pseudodifferential operators on a product of two closed smooth
manifolds, we show the equivalence of their ellipticity (defined by the
invertibility of certain associated homogeneous principal symbols) and their
Fredholm mapping property in associated scales of Sobolev spaces. We also prove
the spectral invariance of these operator classes and then extend these results
to the even larger classes of Toeplitz type operators.Comment: 21 pages. Expanded sections 3 and 4. Corrected typos. Added
reference
Analytic and Reidemeister torsion for representations in finite type Hilbert modules
For a closed Riemannian manifold we extend the definition of analytic and
Reidemeister torsion associated to an orthogonal representation of fundamental
group on a Hilbert module of finite type over a finite von Neumann algebra. If
the representation is of determinant class we prove, generalizing the
Cheeger-M\"uller theorem, that the analytic and Reidemeister torsion are equal.
In particular, this proves the conjecture that for closed Riemannian manifolds
with positive Novikov-Shubin invariants, the L2 analytic and Reidemeister
torsions are equal.Comment: 78 pages, AMSTe
Conormal distributions in the Shubin calculus of pseudodifferential operators
We characterize the Schwartz kernels of pseudodifferential operators of
Shubin type by means of an FBI transform. Based on this we introduce as a
generalization a new class of tempered distributions called Shubin conormal
distributions. We study their transformation behavior, normal forms and
microlocal properties.Comment: 23 page
Longitudinal effect in the dependence of the critical frequency of the midlatitude E layer on solar activity
Variations in the critical frequency of the E layer, foE, measured at Boulder and Tashkent stations located at almost coinciding geographical latitudes but at strongly different geomagnetic latitudes are analyzed. The following conclusions are drawn. (a) Late in the fall and in the winter, the foE values at these stations are distinctly different at low solar activity. This difference decreases with increasing solar activity. In other words, the longitudinal effect in the foE dependence on solar activity is significant for these conditions. (b) This effect is almost absent in summer; i.e., the difference in foE dependence on solar activity at these stations is insignificant for the given season. It has been substantiated that the dependence of the nitric oxide concentration [NO] on geomagnetic latitude, season, and solar activity is one of the main causes of this longitudinal effect. © Pleiades Publishing, Ltd. 2007
Properties of the F2-layer critical frequency median in the nocturnal subauroral ionosphere during low and moderate solar activity
© 2016, Pleiades Publishing, Ltd.Based on an analysis of data from the European ionospheric stations at subauroral latitudes, it has been found that the main ionospheric trough (MIT) is not characteristic for the monthly median of the F2-layer critical frequency (foF2), at least for low and moderate solar activity. In order to explain this effect, the properties of foF2 in the nocturnal subauroral ionosphere have been additionally studied for low geomagnetic activity, when the MIT localization is known quite reliably. It has been found that at low and moderate solar activity during night hours in winter, the foF2 data from ionospheric stations are often absent in the MIT area. For this reason, a model of the foF2 monthly median, which was constructed from the remaining data of these stations, contains no MIT or a very weakly pronounced MIT
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